The purpose of the Clock of the Long Now is to construct a timepiece that will operate with minimum human intervention for ten millennia. It is to be constructed of durable materials, to be easy to repair, and to be made of largely valueless materials in case knowledge of the clock is lost or it is deemed to be of no value to an individual or possible future civilization; in this way it is hoped that the Clock will not be looted or destroyed. Its power source (or sources) should be renewable but similarly unlootable. A prototype of a potential final clock candidate was activated on December 31, 1999, and is currently on display at the Science Museum at London.